This invention relates to a process for the separation of ethylene-containing hydrocarbon mixtures by rectivication at low temperatures. In particular, the invention relates to an improvement in a process wherein the ethylene-containing mixture is separated into a liquid reboiler fraction and an gaseous head fraction; the head fraction is heated, compressed, and partially liquefied in heat exchange with the reboiler fraction which is heated during this step. The resultant liquid is then expanded, and in part, returned as reflux to the rectification, and in part withdrawn as product ethylene.
An ethylene-ethane separation is normally a step at the end of a low-temperature process for the separation of hydrocarbons. The thermal conditions required for reboiler heating and head cooling in the ethylene column can be realized with the aid of a heat pump system. It is thus known from U.S. Pat. No. 3,260,057 to warm the part of the head gas of the ethylene column, to compress the heated gas, to cool the compressed gas countercurrently to itself, to condense cooled gas and to subcool resultant condensate, and then after expansion, to recycle the condensate into the ethylene column as reflux. The residual portion of the head product is withdrawn as gaseous ethylene.
A disadvantage of this conventional process is that the heating of the reboiler fraction takes place solely by liquefaction of the reflux. This means that there is little flexibility to operate and control the heat balance of this process.